Method and apparatus for testing clean room filtration efficiency



Aug. 4, 1970 J. v. KNAB 3,522,724

METHOD AND APPARATUS Fon TESTING lCLEAN RooM FILTRATION EFFICIENCY FiledMarch 29. 1968 United States Patent Office 3,522,724 Patented Aug. 4,1970 3,522,724 METHOD AND APPARATUS FOR TESTING CLEAN ROOM FILTRATIONEFFICIENCY James V. Knab, Grand Rapids, Mich., assignor to WeberShowcase & Fixture Co., Div. of Walter Kidde & Company, Inc., GrandRapids, Mich., a corporation of New York Filed Mar. 29, 1968, Ser. No.717,345

Int. Cl. G01m -/20 U.S. Cl. 73-40.7 4 Claims ABSTRACT OF THE DISCLOSUREA clean room having a series of air diffusing units across one surfacethereof, the individual units being fed by compressed air ducts which,ordinarily, are each connected to a series of the units. Each of theunits is provided with two scalable apertures for access into theinterior thereof. Smoke is introduced into the individual diffuser unitsthrough one o f the apertures and the smoke concentration within theunit is monitored through the other of the apertures. The exterior ofthe unit is then scanned utilizing conventional photometer techniques.Each unit, thus, can be tested individually and it is not necessary tofill the entire system with smoke as required in the past.

-This invention relates to clean rooms and, more particularly, to amethod of and apparatus for testing clean room filtration efficiency.

It is often desirable and/or necessary in the art of' i environmentalcontrol to provide a room, specific area or the like whereintemperature, humidity and dust conditions are maintained withinprescribed limits. Suchenvironments are necessitated, for example, inthe manusearch 'and development has been expended to providesatisfactory environment control for specialized operations such asthose noted` It is not unusual, for example, for a manufacturingtechnique to require that the dust level within the assembly area bereduced to a virtually nonexistent level and this reduction isaccomplished ordinarily by the process of filtering the air entering theparticular area in question through high efficiency filters.

In U.S. Pat. No. 3,323,437 there is illustrated a mode of clean roomconstruction wherein the ceiling of the particular room in question isformed from a plurality of side-by-side air filtration units. Each ofthe units comprises an air plenum with a high-efiiciency filterpositioned across the room-abutting surface thereof. The filters,ordinarily, have particle efficiencies exceeding 99.97 percent for 0.3micron diameter particles vas determined by the Chemical Corp D.O.P.tests.

It is customary in the installation of such rooms to prefabricate asmany of the parts as possible prior to their actual installation at thejob site such that manufacturing tolerances may be controlledeffectively to insure satisfactory operating characteristics subsequentto installation. The patent noted above, thus, contemplates thepre-fabrication of the air diffuser units within the suppliersmanufacturing facility prior to its actual installation at the job site.Once the diffusers have been transported and positioned, elongatedsupply `ducts are connected to the intakes thereof, one such ductusually being utilized to supply compressed, pre-filtered air toalseries of the diffuser units in a line or the` like. Installationspecifications invariably require that, subsequent to completion of theinstallation, a test be run as a means of insuring that all of thefilters are in proper operating condition and, thus, that there 'existsno means within the room wherethrough contaminated matter may gainaccess. These tests are accomplished, ordinarily, by introducing dioctylphthalate smoke into the air circulation system. The filter surfaces andtheir connection with the plenum units are then scanned with aphotometer to detect any excessive amount of leakage.v

It has been'the practice in the past, during the testing of the filtersin the manner described, to introduce the smoke into the air circulationsystem near the fans supplying one particular air duct. The smoke istransmitted to the individual diffusers via the supply duct and, ofcourse, it is necessary to keep at least that duct and all of the filterunits communicating therewith filled with smoke at the properconcentration until each of the diffuser units can be scanned with aphotometer. Photometer scanning, as will be readily appreciated, is arather long and drawn out process and, consequently, it has beennecessary "to retain the smoke charge within an appreciable portion ofthe clean room filtration system for rather lengthy periods. In additionto the length of time which the smokemust be kept in the system, it ishighly difficult, if not impossible, to determine the smokeconcentration within a 'given unit during the testing thereof and it isvery possible that a unit will be tested without having theconcentration of smoke therein up to the specification level. Thislatter problem of course, results occasionally in the approval of a unitwhich, in reality, would not have been approved had the proper smokeconcentration been present within the indivdual plenum during testing ofthe specific diffuser unit.

It is an object of this invention, therefore, to provide a method andapparatus for testing clean room filtration efficiency `which is notsubject to the disadvantages noted above.

More particularly, it is an object of this invention to provide such amethod and apparatus wherein the individual air diffuser units arefilled with smoke to the proper concentration only during the period inwhich they are being scanned and, thus, wherein valuable filter life isnot reduced needlessly during the testing procedure.

It is yet another object of this invention to provide a method andapparatus for monitoring the smoke concentration within the individualdiffuser units during the scanning thereof and, thus, wherein allnon-acceptable uints can be readily detected during the testing process.

It is yet a further object of this invention to provide such a methodand apparatus wherein the filtration efiiciency test can be accomplishedquickly and positively providing a marked reduction in the amount oflabor involved inthe testing procedure as well as the amount of smokeutilized therefor.

`It is a more specific object of this invention to provide an airdiffuser apparatus incorporating integrally therein means whereby thesmoke may be introduced into the interior of the unit during the testingprocedure and, additionally, whereby the smoke concentration may beconstantly monitored.

'Ihese as well as other objects of this invention will be readilyapparent to those skilled in the art by reference to the followingspecification and accompanying figures in which:

FIG. l is a side-elevation view, partially in cross-section, of anillustrative clean-room installation;

FIG. 2 is a plan view of a diffuser unit similar to that illustrated inthe patent noted above which has been modified in accordance with theteachings of the instant invention;

FIG. 3 is a cross-sectional view taken along plane III- 111 of FIG. 2;

FIG. 4 is a cross-sectional view taken along plane IV-- IV of FIG. 2;and

FIG. 5 is a fragmentary view of the aperture sealing structure.

Briefly, this invention comprises a method of and apparatus for testingthe filtering effectiveness of an air diffuser including a plenum with afilter positioned across one portion thereof. The method and apparatuscontemplate the provision of a first sealable aperture into the interiorof the diffuser through which smoke is injected directly into thediffuser unit. Subsequent to completion of the scanning of the exposedportion of the exterior surface of the diffuser to ascertain theexistence of excessive smoke leakage and, thus, the acceptability of theunit, the aperture is sealed off. -In its more specific form, thisinvention contemplates additionally the provision of a second sealableaperture into the interior of the diffuser, the second aperture beingutilized to monitor the concentration of smoke within the diffuserduring the scanning process.

Referring now to the figures, a preferred embodiment of this inventionwill be described in detail. FIG. l illustrates a typical clean-roominstallation having a series of pedestals 11 positioned upon the subfloor of the particular enclosure within which the room is assembled.Mounted upon the pedestals 11 in conventional fashion are a series ofperforate fioor panels 12 from which walls 13 extend vertically.

Conventional construction techniques provide for the assembly of a gridwork of inverted T bars across the ceiling of the room and these barsare utilized to support the light fixtures 14 and the individualdiffuser units 20. The diffuser units 20 are fed by means of a supplyduct 15 into which compressed air is pumped by fan 16. The air isprefiltered by means of filters 17 prior to being taken into the intakeof fan 16.

As will be readily understood by those skilled in the art, FIG. lillustrates only a single row of plenum units 20 within the particularclean-room. Several such rows, ordinarily, would be positioned inside-by-side relationship to form the ceiling of the particularinstallation. Each of the rows is provided with its own supply duct andpressurization fan 16.

The operation of the clean-room, briefiy, involves the laminar diffusionof air through the diffuser units in a downward fashion. This air passesthrough the perforate oor panels 12 into the return air plenum 18. Theair is then drawn to the side of plenum 18 as illustrated in FIG. lthrough the prefilter and back into the intake of fan 16. Prescribedquantities of conditioned air are introduced into the system during thisprocess via the inlet 19.

Referring now to FIGS. 2 through 4, the diffuser units 20 each comprisea stack 21 to which the supply duct 15 is connected during theinstallation process. From the stack 21 there extends in smoothlydiverging fashion a plenum envelope 22 which is fabricated, preferably,of plastic. The plenum envelope 22 terminates in a rectangular filterreceptacle 23 (formed integrally with the envelope 22) within which ispositioned the filter 24. Filter 24, as -will be readily appreciated bythose skilled in the art, must be sealed virtually perfectly to theedges of the filter receptacle 23. To this end, the interior of thefilter receptacle 23 is bordered with wooden strips to which the filteredge is glued by means of a suitable construction sealant. If desirable,a retaining grill as illustrated in the patent noted heretofore may beutilized to assist in the retention of the filter within filterreceptacle 23.

The exterior surface of plenum envelope 22, preferably, is coated withan insulation such as a foamed vinyl in order to minimize heat loss,sweating and the like during operation. This coating, as will be readilyappreciated, may be omitted in certain types of operative environments.

The air diffuser unit 20 is provided with an air volume controlassembly. 'Ihe control assembly consists of an aperture 31 through thefilter or the filter-connecting strip in the event it is necessary toutilize two or more filters within the receptacle. Within the apertures31 is suspended an elongated shaft 32 which ties directly to a bi-valvedamper assembly 33. The downward extremity of shaft 32 is provided witha slot for reception of a screwdriver or other suitable tool and, byrotating the shaft 32, the dampers 33 are caused to close and open bymeans of a conventional worm gear assembly. A fiexible plug 34, such asthat to be discussed in connection with FIG. 5, is provided for sealingthe aperture 31 subsequent to adjustment of the damper assembly 30.

As described to this point, the filter diffuser unit 20 is identical tothe unit described in detail in U.S. lPat. No. 3,323,437, notedpreviously. The instant invention relates to the incorporation withinthe diffuser unit 20 of a smoke input aperture 40 and a smoke monitoringaperture 45. These apertures, preferably, are positioned within thefilter 24 or the connecting strip in the manner illustrated in order topermit testing of the unit from the interior of the room rather thanrequiring the provision of walk ways and the like overhead. As will bereadily apparent to those skilled in the art, however, the aperturescould be placed elsewhere in the diffuser unit such as in the plenumenvelope 22 when convenient.

The aperture 40 comprises a hollow sleeve 41 which is positioned withinand glued to the sides of the filter in a manner similar to the sleeveutilized in conjunction with the damper control shaft 32. The sleeve 41is provided with a removable plug 42. The smoke monitoring aperture 45,similarly, comprises a sleeve 46 positioned within filter 24 having acap 47 removably positioned thereover.

Where, for the reasons noted there is a Wooden strip across the plenumunit separating two filters, apertures 40 and 45 may be drilled directlythrough the strip. In this event, of course, it is not necessary toutilize sleeves within the apertures. Such a structure is illustrated,for example, in FIG. 5.

Subsequent to installation of the units in the manner illustrated inFIG. l, one of the fans 16 is activated. Each of the filters are thentested by removing the caps 42 and 47 therefrom. Smoke is fed into theinterior 28 of plenum envelope 22 via aperture 40. This smoke, as noted,will ordinarily be dioctyl phthalate having a 0.3 micron dispersionfactor. 'Installation specifications will require ordinarily that thesmoke concentration within the envelope 22 be maintained at or above aspecified figure-ie. micrograms per liter or equivalent of a No. 4 onthe Sinclair Phoenix Photometer-during the testing procedure. Theinstant invention permits monitoring of the smoke concentration withinthe plenum 28 by means of the aperture 45.

As smoke is inserted into the interior plenum 28 via aperture 40, thus,and its concentration monitored by a probe or the like through aperture45, the exterior surface of the filter as well as its connection to thereceptacle 23 are scanned by means of a photometer in conventionalfashion. Subsequent to completion of the tests, the plugs l42 and 47 arereinserted into the apertures 40 and 45 to seal them and the particulardiffuser unit is ready for use. The process is then repeated with eachof the diffuser units in the particular installation and, if necessary,they are replaced or repaired until such time as the entire room isready for use.

FIG. 5 illustrates a plug 42 or 47 suitable for use in conjunction withthe practice of the instant invention. This plug, as noted previously,is positioned within an aperture in a wooden joining strip as opposed towithin a sleeve such as those indicated at `41 and 46 passing directlythrough the filter. The plug has a cylindrical section 51 with ashoulder 52 extending outwardly from the downward extremity thereof.Sections 51 and 52 are integrally formed from rubber, polyvinyl chlorideor some other elastic material. The upper extremity of section 51 haspositioned therein and joined thereto a nut 53 into which is threaded ascrew 54. The head 55 of screw 54 rests on shoulder 52. The relaxeddiameter of section 51 slightly less than the diameter of the apertureto be sealed.

When testing of a particular unit has been completed, the plug isinserted into the aperture and the screw 54 tightened to draw nut 53toward shoulder 52. Since nut 53 is bonded to the section 51, suchdrawing causes cylindrical section 51 to expand in diameter, tightlysealing the aperture.

By utilizing the teachings of the instant invention, it will be apparentreadily that each of the diffuser units may be tested without fillingthe entire system with smoke as required previously. The head of air atthe stack 21 will prevent nearly all, if not all, of the smoke fromfinding its way into other diffuser units during the testing processand, thus, other filters will not be needlessly contaminated. Theinstant invention provides, additionally, a means whereby the smokeconcentration within the unit being tested may be monitored to insurethat is it up to specification. This invention, thus, provides a methodand apparatus whereby the filtering effectiveness may be tested moreeasily and more accurately than has been possible heretofore.

While a preferred embodiment of this invention has been described indetail, it will be readily apparent to those skilled in the art thatother embodiments may be conceived and fabricated without departing fromthe spirit and scope of the instant specification and accompanyingdrawings.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A method of testing the filtering effectiveness of a series ofclosely adjacent air diffusers connected to a common supply duct, eachdiffuser including a plenum with a filter positioned across one portionthereof and having a compressed air intake thereinto, said method havingthe steps of:

providing first and second sealable aperturesy into the interior of saiddiffusers;

pressurizing positively the plenums of the diffusers to be tested bymaintaining the pressure in said duct at a level exceeding both ambientpressure and the pressure within said plenums;

injecting smoke into the interior of the particular diffuser which isbeing tested through one of the apertures therein;

confining by means of said plenums and the pressure differential betweensaid duct and said plenums the smoke so injected to the interior of theparticular diffuser which is being tested;

scanning at least portions of the exterior surface of said diffuser toascertain the existence of any smoke leakage therefrom;

metering the concentration of smoke within the interior of the diffuserwhich is being tested through the other of said apertures during thescanning thereof;

and sealing said apertures prior to utilization of the diffuser. 2. Aclean room suitable for specialized electronic production, medicalsurgery and the like comprising a plurality of closely adjacent airdiffuser means positioned along one surface thereof, each of saiddiffuser means having a plenum chamber with a filter positioned acrossone surface thereof and having a compressed air intake thereinto, aseries of said diffuser means having their respective intakes connectedto common supply lines, the pressure in each said supply line exceedingthe pressure in the plenum chambers connected thereto when said room isin operation, first sealable aperture means opening to the interior 0feach said diffuser means wherethroughV smoke may be introduced into theinterior of each said diffuser means for purposes of testing thefiltering effectiveness thereof; second sealable aperture means openingto the interior of each said diffuser means Wherethrough the smokeconcentration within each of the diffuser means may be monitored duringtesting thereof; and, means for sealing said first and second aperturemeans after testing and monitoring has been completed.

3. The structure as set forth in claim 2 wherein said first aperturemeans extend through the room-facing surfaces of said diffuser means.

4. The structure as set forth in claim 3 wherein said second aperturemeans extend through the room-facing surfaces of said diffuser means.

References Cited UNITED STATES PATENTS 1,933,791 11/1933 Crouch 73-40.7X 3,323,437 6/1967 Knab 98-40 3,364,729 1/ 1968 Yearwood 73-40.73,395,514 8/196'8 Bub 73-40.7 X

FOREIGN PATENTS 184,35 8 5 1955 Germany.

OTHER REFERENCES New Techniques in the Testing of HEPA Filters, byRobert H. Avery, Air Engineering, January 1968, pages 14-18.

S. CLEMENT SWISHER, Primary Examiner H. C. POST III. Assistant ExaminerU.S. Cl. X.R.

